There are many instances when it is highly desirable to be able to measure accurately the magnitude of a load applied to a vehicle, a ship, a floating buoy, or some other transportation device. This is especially so if measurements are being taken, or something is being towed. For example, in the process of mineral exploration, magnetometers or other similar devices are frequently dragged in the air behind an aircraft, or in the sea behind a ship. The body being towed normally comprises a complex package of electronic instrumentation. Thus, it would be highly desirable to know accurately the kinds of vertical loads applied to the towed body, the towing cable, or any couplings connecting that cable either to the towed body or the "towing vehicle". When aerial surveys are conducted, for example, in hilly terrain or where the topography of the land includes many lakes, rivers or valleys, air turbulence is frequently encountered. The same sort of buffetting will apply, of course, to the vertical motion caused by waves on a lake or ocean.
The measurement of vertical acceleration loads is frequently made in the "towing vehicle". This, one must take into account pitching and rolling motions of that vehicle. In other words, it is an accurate measurement of the vertical component of the applied load which is most frequently of concern. That vertical component must therefore be isolated or separated from non-vertical components of the load or force applied to the "towing vehicle". One technique for eliminating the non-vertical components of a load applied to the towing vehicle is the use of stabilized platforms. Such platforms, however, are relatively bulky, are costly, and have an operating life span of perhaps three hundred hours mean time between breakdowns. Moreover, using a stabilized platform requires a much higher level of maintance skill, with its attendant higher costs. Further yet, the provision of spare units for backup purposes would also be costly.